The aim of this paper is to analyze energy pathways for a fossil fuel rich developing country towards an energy transition considering national and international oil availability using Ecuador as a reference. An integrated assessment model has been developed to simulate energy transition scenarios considering constraints on oil availability at the national and global level. Results show that if current trends in energy demand and supply persist, energy scarcity would start around 2040 due to depletion of national oil reserves and restricted access to foreign oil. This would trigger a degrowth in economic activity in sectors with high dependency on petroleum products. Scenarios with conservative efforts might partially revert the increasing use of fossil fuels supported by policies for energy efficiency and substitution of liquid fuels with electricity mainly from renewables. However, energy shortages would still be foreseeable as well as a decay of the economy. Under a maximum efforts scenario with an optimistic availability of national oil, a moderate-sustained economic growth could be feasible. This shows that oil would still play a key role during the transition. Furthermore, ambitious policies must be implemented in the short term to smooth the effects of displacing oil as energy and income source.